User Manual

EP7309/11/12 User’s Manual - DS508UM4 2-13

CPU Core

logic (CLKEN) pin can be used to disable external oscillator if desired. In

this configuration,

•RTCremainson.

Entering standby state can be accomplished in software by writing to the STDBY

nURESET or by nPWRFL.

Before entering the standby state, the software must properly disable the DAI. Failing

to do so will result in higher than ex pected power consumption wh ile in this state as

well as unpredictable behavior of the DAI.

During standby state, all system memory and s tate are maintained and the system

time is kep t up-to-date. Th e external address and data bus a re forced low internally

by the

RUN signal which is also driven low. This is don e to prevent peripherals that

are powered down from draining current. Since the

RUN signal is driven low, it can

also be used to disable external devices to further reduce power drain wh ile in th is

state. The internal peripherals external signals retur n to their reset s tate.

Exiting standb y is accom plished with the following external stimulus of a keyboard

interrupt (if enabled), power management inputs, external interrupts

EINT[3:1],or

WAKEUP.

The following register will allow the system software to put the processor into

Standby state. Writing to this loca tion will not clear the internal registers settings of

the processor. The processor will sit u n til an ex tern al interrupt or the

WAKEUP pin is

asserted and continue executing code from the point of entry into Standby.

State Control Register Descriptions

Enter the Standby State Register (STDBY)

Address: 0x8000.0840, Write Only

Definition: A write to this location will p u t the sys tem into the Standby State by

halting the main oscillator. A write to this location while there is an

active i nterrupt will have no effect.

Note: Before entering the Standby State, the LCD Controller should be disabled. The

LCD controller should be enabled on exit f rom the Standby State. If the EP73XX

is attempting to get into the Standby State when there is a pending interrupt

request, it will not ent er into the low power mode. The instruction will get

executed, but the processor will ignore the command.

Idle State

From operating state, the processor can enter Idle state by writing to the HALT

operating state and execute th e next instruction.

WAKEUP cannot be used.

In th e Idle state, the device will function as i t would in operating state with the

exception of the CPU clock which is halted. The PLL (if enabled) or the external

13 MHz clock source will remain active during this state.